SpringBoot中日志加载的全链路拆解

logging:
  level:
    com.example: debug
  pattern:
    console: "%d{yyyy-mm-dd hh:mm:ss.sss} [%thread] %-5level %logger{36} - %msg%n"

<dependency>
    <groupid>org.springframework.boot</groupid>
    <artifactid>spring-boot-starter-logging</artifactid>
</dependency>

// slf4j 内部（简化）
public static iloggerfactory getiloggerfactory() {
    // 通过类加载找到 staticloggerbinder 单例
    return staticloggerbinder.getsingleton().getloggerfactory();
}

// 简化流程
class loggingapplicationlistener implements applicationlistener {

    void onapplicationevent(event) {
        // 1. 检测 loggingsystem 实现
        loggingsystem system = loggingsystem.get(classloader);
        // logback → logbackloggingsystem
        // log4j2 → log4j2loggingsystem
        // 无 → nooploggingsystem

        // 2. 应用前初始化（beforeinitialize）
        system.beforeinitialize();

        // 3. 读 application.yml 中的 logging.* 配置
        // 4. 应用初始化（initialize）
        system.initialize(loggingproperties);
    }
}

class logbackloggingsystem extends abstractloggingsystem {

    void initializewithconventions() {
        // 如果用户提供了 logback-spring.xml → 用它
        // 如果用户提供了 logback.xml → 用它
        // 否则 → 用 spring boot 默认的 logback 配置模板
        //       （spring-boot.jar 里的 base.xml / defaults.xml）
    }
}

logging:
  level:
    root: info
    com.example: debug
    com.example.service: warn
    org.hibernate: error

// logbackloggingsystem 核心逻辑（简化）
void configureloggerlevels(string name, loglevel level) {
    logger logger = loggercontext.getlogger(name);
    logger.setlevel(ch.qos.logback.classic.level.valueof(level.name()));
}

# 查看当前 logger 级别
get /actuator/loggers/com.example

# 动态修改级别（无需重启）
post /actuator/loggers/com.example
{
  "configuredlevel": "debug"
}

// loggersendpoint → loggingsystem → logbackloggingsystem
void setloglevel(string loggername, loglevel level) {
    // 直接调用 logback api
    logger logger = loggercontext.getlogger(loggername);
    logger.setlevel(convert(level));
}

logging:
  file:
    name: /var/log/app/app.log
    max-size: 100mb
    max-history: 30
    total-size-cap: 3gb
    clean-history-on-start: true

<appender name="file" class="ch.qos.logback.core.rolling.rollingfileappender">
    <file>/var/log/app/app.log</file>
    <rollingpolicy class="ch.qos.logback.core.rolling.sizeandtimebasedrollingpolicy">
        <filenamepattern>/var/log/app/app.%d{yyyy-mm-dd}.%i.log</filenamepattern>
        <maxfilesize>100mb</maxfilesize>
        <maxhistory>30</maxhistory>
        <totalsizecap>3gb</totalsizecap>
        <cleanhistoryonstart>true</cleanhistoryonstart>
    </rollingpolicy>
    <encoder>
        <pattern>...</pattern>
    </encoder>
</appender>

<configuration>
    <!-- 生产环境：输出到文件 + error 级别 -->
    <springprofile name="prod">
        <root level="error">
            <appender-ref ref="file"/>
        </root>
    </springprofile>
    <!-- 开发环境：控制台 + debug -->
    <springprofile name="dev">
        <root level="debug">
            <appender-ref ref="console"/>
        </root>
    </springprofile>
</configuration>

<configuration>
    <!-- 从 application.yml 读取属性 -->
    <springproperty name="app_name" source="spring.application.name" defaultvalue="app"/>
    <springproperty name="log_path" source="logging.file.path" defaultvalue="/var/log"/>
    <appender name="file" class="ch.qos.logback.core.rolling.rollingfileappender">
        <file>${log_path}/${app_name}.log</file>
    </appender>
</configuration>

mdc.put("traceid", "abc123");
log.info("处理请求"); // 输出：2026-08-07 ... [traceid=abc123] 处理请求
mdc.remove("traceid");

@component
public class tracefilter implements filter {

    @override
    public void dofilter(servletrequest req, servletresponse resp, filterchain chain)
            throws ioexception, servletexception {
        string traceid = uuid.randomuuid().tostring().replace("-", "");
        mdc.put("traceid", traceid);
        mdc.put("path", ((httpservletrequest) req).getrequesturi());
        try {
            chain.dofilter(req, resp);
        } finally {
            mdc.clear(); // 必须！线程池复用会泄露
        }
    }
}

<pattern>%d{yyyy-mm-dd hh:mm:ss.sss} [%x{traceid}] [%thread] %-5level %logger{36} - %msg%n</pattern>

map<string, string> mdccontext = mdc.getcopyofcontextmap();

completablefuture.runasync(() -> {
    if (mdccontext != null) {
        mdc.setcontextmap(mdccontext);
    }
    try {
        log.info("异步任务执行");
    } finally {
        mdc.clear();
    }
});

@configuration
public class asyncconfig {

    @bean
    public taskexecutor taskexecutor() {
        threadpooltaskexecutor executor = new threadpooltaskexecutor();
        executor.setcorepoolsize(4);
        executor.settaskdecorator(new mdctaskdecorator());
        return executor;
    }
}

public class mdctaskdecorator implements taskdecorator {
    @override
    public runnable decorate(runnable runnable) {
        map<string, string> contextmap = mdc.getcopyofcontextmap();
        return () -> {
            try {
                if (contextmap != null) {
                    mdc.setcontextmap(contextmap);
                }
                runnable.run();
            } finally {
                mdc.clear();
            }
        };
    }
}

public class userturbofilter extends turbofilter {

    @override
    public filterreply decide(marker marker, logger logger, level level,
                              string format, object[] params, throwable t) {
        string user = mdc.get("userid");
        if ("debug-user-123".equals(user) && level.isgreaterorequal(level.debug)) {
            return filterreply.accept; // 强制接受
        }
        return filterreply.neutral; // 不干预，走正常 level 判断
    }
}

<turbofilter class="com.example.logging.userturbofilter"/>

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <!-- 引入 spring 属性 -->
    <springproperty name="app_name" source="spring.application.name" defaultvalue="app"/>
    <springproperty name="log_path" source="logging.file.path" defaultvalue="/var/log"/>
    <!-- 控制台 appender：带 traceid -->
    <appender name="console" class="ch.qos.logback.core.consoleappender">
        <encoder>
            <pattern>%d{yyyy-mm-dd hh:mm:ss.sss} [%x{traceid:-}] [%thread] %-5level %logger{36} - %msg%n</pattern>
            <charset>utf-8</charset>
        </encoder>
    </appender>
    <!-- 文件 appender：滚动 + 压缩 -->
    <appender name="file" class="ch.qos.logback.core.rolling.rollingfileappender">
        <file>${log_path}/${app_name}.log</file>
        <rollingpolicy class="ch.qos.logback.core.rolling.sizeandtimebasedrollingpolicy">
            <filenamepattern>${log_path}/${app_name}.%d{yyyy-mm-dd}.%i.log.gz</filenamepattern>
            <maxfilesize>200mb</maxfilesize>
            <maxhistory>30</maxhistory>
            <totalsizecap>5gb</totalsizecap>
            <cleanhistoryonstart>true</cleanhistoryonstart>
        </rollingpolicy>
        <encoder>
            <pattern>%d{yyyy-mm-dd hh:mm:ss.sss} [%x{traceid:-}] [%thread] %-5level %logger{36} - %msg%n</pattern>
            <charset>utf-8</charset>
        </encoder>
    </appender>
    <!-- error 独立文件：快速定位错误 -->
    <appender name="error_file" class="ch.qos.logback.core.rolling.rollingfileappender">
        <file>${log_path}/${app_name}-error.log</file>
        <filter class="ch.qos.logback.classic.filter.thresholdfilter">
            <level>error</level>
        </filter>
        <rollingpolicy class="ch.qos.logback.core.rolling.sizeandtimebasedrollingpolicy">
            <filenamepattern>${log_path}/${app_name}-error.%d{yyyy-mm-dd}.%i.log.gz</filenamepattern>
            <maxfilesize>100mb</maxfilesize>
            <maxhistory>60</maxhistory>
            <totalsizecap>2gb</totalsizecap>
        </rollingpolicy>
        <encoder>
            <pattern>%d{yyyy-mm-dd hh:mm:ss.sss} [%x{traceid:-}] [%thread] %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    <!-- 按环境切换 -->
    <springprofile name="dev">
        <root level="debug">
            <appender-ref ref="console"/>
        </root>
    </springprofile>
    <springprofile name="prod">
        <root level="info">
            <appender-ref ref="file"/>
            <appender-ref ref="error_file"/>
        </root>
        <!-- 框架日志降噪 -->
        <logger name="org.springframework" level="warn"/>
        <logger name="org.hibernate" level="warn"/>
        <logger name="org.apache.kafka" level="warn"/>
    </springprofile>
</configuration>

<logger name="com.example" level="debug" additivity="false">
    <appender-ref ref="file"/>
</logger>

<appender name="async" class="ch.qos.logback.classic.asyncappender">
    <queuesize>1024</queuesize>
    <discardingthreshold>0</discardingthreshold> <!-- 0=永不丢弃 -->
    <neverblock>false</neverblock> <!-- 队列满时阻塞而非丢弃 -->
    <appender-ref ref="file"/>
</appender>

# 启动时加 -dlogback.debug=true 可以看到 logback 初始化全过程
java -dlogback.debug=true -jar app.jar